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00:00The outcome of World War II is at stake.
00:07Over 400 American and Japanese warships do battle at Leyte Gulf.
00:13It was the largest naval action in history.
00:17Japan is counting on a secret weapon the Americans know almost nothing about,
00:23except her name, Musashi.
00:26You'll find in the summer of 1944 the naval intelligence experts groping for an understanding of these huge ships.
00:35At 72,000 tons, she's the largest battleship ever built.
00:40She's not just 10% bigger than some of these other vessels, she's nearly double.
00:45Bristling with anti-aircraft batteries and massive 18-inch guns.
00:51You can't believe all the firepower that comes up at one time.
00:58Her builders boast she's unsinkable.
01:02Yet, in her first major fight, this super battleship is sent crashing to the ocean floor.
01:09But mysteries have always surrounded Musashi.
01:18Now, Americans and Japanese researchers are joining forces to unlock her most stubborn secrets.
01:28This front part is where flooding is taking place.
01:35Why did an unsinkable giant go down so fast?
01:40Was it overwhelming American air power?
01:43Or a fatal design flaw that sent nearly 1,000 Japanese sailors to their death?
01:50Hundreds of people are crying for help in horrified voices as they were all sucked into the waves.
02:01To unravel the mysteries of Musashi, the missing giant must first be found.
02:08In February 2011, a research vessel begins a three-week expedition in the Cebuyan Sea of the central Philippines.
02:27You know, if this was anywhere else, you'd see the whole coastline would have been changed.
02:32With buildings and high rises and all sorts of things, and that's not the case here.
02:36So we know we're looking at basically what the pilots saw 70-odd years ago.
02:43The expedition is the brainchild of the late Paul Allen, co-founder of Microsoft.
02:50The son of a World War II veteran, Allen committed significant resources to searching for the war's most iconic missing shipwrecks.
02:59Among them, the mysterious Musashi.
03:02Rob Craft is in charge of conducting all subsea operations.
03:09The Musashi was the pride of the Japanese fleet.
03:14It was so important to the Japanese people that they didn't even form the population that it had sunk.
03:20Lots of people would like to find the Musashi. It's one of the great battleships. It's one of the truly remarkable ones that haven't been found.
03:29David Mearns has made a career out of hunting for lost shipwrecks.
03:33After months spent combing through military archives in the U.S. and Japan.
03:40And what it's showing you here...
03:42He's identified the critical clues he hopes will lead them to Musashi.
03:46This is that one.
03:48One is visual.
03:51Aerial photographs taken by American pilots during their final devastating attack.
03:57There's the plane coming in, lining up right there to attack Musashi.
04:04And this is the next frame in the sequence.
04:07We can no longer see the plane, but we see a torpedo head.
04:09Clearly recognizable in the background of these photographs is the outline of Cebuyan Island, a few miles to the south.
04:22Outside this, sir.
04:23Outside the blue circle.
04:24Outside the blue.
04:25Yeah.
04:26Yeah.
04:27But there are other clues that may narrow down the search even further.
04:32And the most important one came from one of the destroyers, a Japanese destroyer that was ordered.
04:38Stand by Musashi.
04:41Kiyoshima actually took a position for Musashi sinking.
04:46Using the position reported by the destroyer, Kiyoshima,
04:50Mearns and Kraft have determined a high probability search area.
04:55The tool selected for the search is called a multi-beam echo sounder.
05:00It's a type of sonar that's mounted on the ship's hull.
05:03An array of downward-looking beams emitting sound waves sweeps across the seabed to create an image of a mile-wide swath.
05:13We're over here on the western side of our box.
05:18We're running the first line to the east.
05:19And this happens to be line number 13.
05:23And each line should take about four hours.
05:27And because we're looking for, in terms of the depth of water, quite a small target,
05:32we're mapping the seabed in very, very high detail.
05:35So the by-product of our search is a really detailed map of this particular part of the Philippines.
05:42Even though Musashi is as big as a 75-story building,
05:47the battleship will only show up as a small speck on this vast and unexplored seafloor.
05:54There's no guarantee she can be found.
05:56It all depends on her orientation on the bottom if she's in one piece, two piece, three pieces.
06:04We should be able to detect that and see that in what they call the backscatter imagery.
06:08When you hit something hard, it shows up as a very, very dark object.
06:11It takes four days to cover the high probability area.
06:20It yields an impressive picture of the seabed below, including a newly discovered seamount.
06:28But so far, there's no sign of Musashi.
06:33So our highest probability to begin with was all on the basis of this Japanese destroyer, Kiyoshima,
06:39which gave a precise sinking position to her.
06:43It's now very clear that that position wasn't as accurate as I had hoped.
06:48And because of that, we're now having to expand the search.
06:54Their focus shifts to the second, albeit less precise clue.
07:00The aerial photographs taken by the American planes attacking Musashi.
07:04I mean, I think if we go, if we go down here, we're going to be able to, we're going to be able to get a better feel.
07:11Yeah.
07:13This cardboard box, which has the same field of view as the camera the airmen used,
07:19allows Mearns to get a close approximation of what they saw.
07:23Musashi would be about two kilometers closer to the island from here during these, when these photographs are taken.
07:29And she sinks four hours later.
07:33With the evidence gleaned from the photos, they plot a new series of sonar runs.
07:39That's what we've covered, that red line there.
07:42Right, right.
07:43Anywhere outside of that, she could be.
07:45I would almost bias it further to the west, because in that photograph, she's clearly heading westerly as opposed to north.
07:54But the clock is ticking.
07:57The expedition only has two weeks left to find the mystery ship.
08:04Musashi was first conceived in the 1930s.
08:08A time when Japan's efforts to expand its territory and influence in Asia and the Pacific
08:14were increasingly blocked by its former ally, the United States.
08:21Japanese national prestige had been dealt an insult by the Washington Naval Treaty.
08:27Just to put it in numbers, the treaty created circumstances where, for every 100 United States warships that are built, the Japanese are permitted 60.
08:35It created a future in which the Japanese Imperial Navy was going to be numerically inferior to the United States Navy.
08:43In response, a powerful faction begins advocating for a different strategy.
08:49Japan at the time had neither the resources nor the budget to build a large number of battleships to fight against the US.
09:03So they decided to counter quantity with quality.
09:07That was the idea they came up with.
09:10Quality meant constructing giant battleships that could overcome the enemy's larger numbers.
09:16The new battleship was called the Yamato class after its prototype.
09:23To win public support, this Navy handbook likens it to a powerful figure in a popular movie of the time.
09:30The Hollywood film about a giant ape creating mayhem in New York was a huge hit with Japanese audiences.
09:45And so the comparison is not just a comparison evocative of power and strength.
09:52It's also kind of pointed squarely at New York City and therefore pointed directly at the Americans.
10:00In March 1938, construction of Musashi began here at the Mitsubishi Shipyard in Nagasaki.
10:10Incredibly, the giant gantry crane that built her is still in use today.
10:19The Japanese virtually had to reinvent naval architecture and design of ships to be able to build such colossal vessels.
10:28Work proceeded under a literal veil of secrecy.
10:35When they were being built, they were actually built behind the gigantic curtains that were raised up in the shipyards.
10:40And so even friendly people couldn't see what was going on behind there.
10:43So there was some attempt to keep it a secret.
10:46A schoolgirl at the time, Ms. Matsura, remembers what it was like.
10:52I was told never to look in the direction of the shipyard, that soldiers are on board keeping watch.
11:01You must not look or the soldiers will take you away.
11:05Even as a child, I kind of sensed that a big war was going to break out.
11:09On December 7th, 1941, that war began.
11:16In its surprise attack on Pearl Harbor, the Japanese Navy used carrier-based air power to devastating effect against the American fleet.
11:26Ironically, that success only reinforced its faith in its own new super battleships.
11:32A lot of the naval theory at the time was based on this fleet-on-fleet engagement.
11:39The Japanese in particular were still hoping for that kind of thing.
11:42This is how you wrest sea control from the other guy. You defeat his fleet.
11:49In August 1942, Musashi began secret sea trials.
11:55Weapons and defenses carefully kept out of sight from enemy spies were put to the test.
12:02Musashi's main armament came in the form of three turrets mounting three Type 94 naval guns.
12:10These were of 18-inch caliber and were therefore the largest naval guns in use anywhere in the world.
12:21To defend herself, Musashi was shielded by the heaviest armor ever used on a ship's hull.
12:28The high-grade steel came from low-phosphorus iron secretly mined in Japanese-occupied Manchuria.
12:35For 19-year-old Masahiro Oesi and the hundreds of young sailors assigned to serve aboard this giant, Musashi was a technological wonder.
12:48We never thought for a second that Musashi would sink and people would die.
12:58He believed that such a giant ship could not be taken down.
13:02To them, she was the King Kong of the sea.
13:13Day 14 of the Musashi search expedition.
13:17At last, the team thinks they're onto something.
13:21Could she be broken in four pieces sitting there?
13:26One of their sonar runs has revealed a promising target.
13:31That is exactly what you want to look for.
13:34Bow, super structure, things falling off the super structure, blah, blah, blah.
13:39Central area, engine room, break here, explosion there, stun.
13:42It's all going to be right there.
13:44Right.
13:45And if it capsized, it's going to be over.
13:51But after making several more sonar runs, they reluctantly reached the conclusion the object is too large.
13:59You know, it's 100 meters bigger than what we're looking for.
14:03Wow.
14:04It's 30% bigger.
14:06I think it's definitely something.
14:08Yeah.
14:09Other than geology.
14:10I don't think it's inside.
14:17After three weeks, the expedition is out of time.
14:21The research vessel must return to port.
14:24But they've covered a staggering 1,400 square miles.
14:28An area as big as the state of Rhode Island.
14:30What we now have is a very highly accurate map of the entire area that we want to search.
14:37We know where she's not.
14:38We've ruled out large sways of the civilian sea.
14:41And their commitment to the task has only intensified.
14:46Everybody's kind of got a lot of blood, sweat and tears in trying to find this track.
14:50You know, you get this personal passion going trying to find this thing.
14:53But to succeed, they must first find a better tool for searching the rugged sea floor below.
15:06By the time Musashi joined the Japanese war effort in the Pacific in 1942, the momentum was about to shift.
15:11The Japanese actually are prevailing at this point because they're better at surface warfare than we are in this early stage in the game.
15:22What then becomes clear is that anytime aircraft carriers get involved, the whole thing changes.
15:27The U.S. embraces naval air power in a way that it just hadn't before.
15:32It revises the way that it trains, it revises tactics and it revises weapons to the extent that it introduces a new fighter, a new dive bomber, a new torpedo bomber and it even introduces a new torpedo.
15:45The Mark 13 torpedo was more reliable and could be dropped at higher altitude than its predecessor.
15:55At the same time, American intelligence secured a valuable lead.
16:01On the island of Tulagi, Americans captured a document that was a warship recognition manual that was to be used by Imperial Navy sailors to recognize their own ships.
16:13And it had a drawing of Yamato class ship.
16:18But after that, nothing.
16:22It's as if Japan's most secret weapon had vanished.
16:27You'll find in the summer of 1944, the naval intelligence experts groping for an understanding of these huge ships.
16:36And they came up with estimates that were just unbelievable.
16:41But as they would later discover, even those estimates were way too small.
16:50By June 1944, American forces succeeded in pushing the Japanese fleet, totaling some 60 ships and 450 aircraft out of the Western Pacific.
17:01The battle became known as the Great Mariana's Turkey Shoot.
17:07They call it that because they harvest so many Japanese aircraft.
17:12They shoot them down wholesale.
17:13The Japanese lose half their carrier strength and they lose almost all of their naval aviation.
17:22American General Douglas MacArthur was now poised to invade the gateway to Japan itself, the Philippines.
17:30On October 20th, MacArthur came ashore on the eastern side of Leyte Island, where American troops encountered little resistance.
17:42The opinion united of American intelligence agencies was that the Japanese Navy would not come out.
17:52We based our ideas on the assumption that the Japanese would need a considerable amount of time to train new aircrew and pilots for their aircraft carrier groups.
18:02But American intelligence was ignoring one critical fact.
18:10Japan's Navy remained committed to fighting a decisive battle at sea.
18:15Its surface fleet was still largely intact, led by two giants Americans had yet to lay eyes on, Musashi and Yamato.
18:24American radio intelligence had knowledge of the movements of these Japanese ships, but still not of their characteristics.
18:36On October 24th, 1944, Admiral Kurita's center force with 26 ships entered the Sibuyin Sea.
18:45Two other slightly smaller Japanese fleets approached from the south and north.
18:50The Battle of Leyte Gulf was about to begin.
18:58In the morning when Kurita's crossing the Sibuyin Sea, the reconnaissance flights picked this up.
19:04And of course, at that point, they're aware they got two very large battleships down here.
19:09American pilots were the first to catch a real glimpse of Musashi and Yamato.
19:14We knew that they had two big battleships. That's about all we knew.
19:20And it was obviously the biggest thing we'd ever seen.
19:24Although caught by surprise, the U.S. Navy was prepared.
19:29Seventh Fleet moved to guard the Leyte landing site itself, while Third Fleet deployed in three groups to the north.
19:36Unfortunately, the one element of the Third Fleet that's closest to San Bernardino Strait is a little bit weaker because it sent one of its carriers off to refuel.
19:46Its sole remaining large carrier was only half the size of the two giants bearing down on it, with 24 more warships in Japan's center force.
19:58In late February 2015, Rob Craft and David Mearns renew their search for Musashi.
20:13Since they were last here, they've found the perfect tool for the difficult task ahead.
20:18It's now installed aboard the expedition yacht Octopus, equipped with state-of-the-art deep-sea equipment.
20:33Their key search tool is still so new, it's rarely been used in the deep ocean.
20:38AUV is an autonomous underwater vehicle. Our AUV is capable of diving down to 1,500 meters.
20:49It takes with it a side-scan sonar system that looks out on the sides and provides us an image of things that may be lying on the seafloor.
20:58Its survey route is selected based on the bathymetric map that systems engineer Wayne Sadowski compiled during the 2011 expedition.
21:09This map is of the, basically the subsea volcano that we're seeing.
21:14And so using this map, we then program the autonomous vehicle.
21:18Traveling two-thirds of a mile down and a few hundred feet above the ocean floor, the AUV maps the terrain.
21:26But distinguishing a man-made object among the rugged volcanic outcrops is challenging.
21:33Because the lava rock is as reflective as the acoustic waves are that we use to bounce off the metal of Musashi.
21:41After 18 hours, the AUV returns to the surface and is brought on board to download the data.
21:48Everybody had a go at looking at the side-scan information.
21:52Everybody, what do you see?
21:54Oh, it's something shiny there.
21:55That's a rock.
21:56No, that's a rock.
21:57No, that's something.
21:58No, that's a rock.
22:00The first AUV survey yields nothing, as does the second.
22:05And I'll tell you that up to that point, we were starting to second guess ourselves.
22:12We had searched a large portion of the primary search area and we weren't finding what we had hoped to find.
22:19On the third run, they finally see something.
22:28Generally, when you're finding a wreck, it's either happening instantaneously, but in this one, it was a bit of a slow burner because the sonar image didn't sort of shout out, this is Musashi, this is where I sank.
22:40It was more of, there was an indication something was there.
22:44Dave, you're pulling in the water.
22:46That's a safe heading.
22:49For a closer look, they launch a remotely operated vehicle, or ROV.
22:54It's smaller than a Volkswagen Bug, but it's still quite substantial, and it's on a cable as well.
23:01But in that cable, it has power conductors and fiber, and through that, we get to watch our HD camera that's on the end of the tether.
23:09It will take the ROV an hour to reach the ocean floor, almost a mile below.
23:17Plenty of time to wonder if at last, they're going to set eyes on Musashi.
23:25On the morning of October 24th, 1944, the skies over the Sebulian Sea were filled with over 40 American warplanes.
23:35The U.S. naval aircraft that opposed the Japanese center force in the Sebulian Sea consists of the Hellcat fighter, the Helldiver dive bomber, and the Avenger torpedo bomber.
23:49The fighters led the way with strafing runs.
23:51You're going to go after the battleships because they are the biggest target.
23:56They can do the most damage to you, therefore you want to take them out.
24:00But the Japanese gunners were ready.
24:04Unleashing a hail of fire from Musashi's 100 anti-aircraft guns.
24:09Arial attacks had become fierce after war broke out, so the decision was made to strengthen anti-aircraft defenses and machine guns were also rapidly added.
24:30But there was no industrial capacity to manufacture bulletproof armor at this point.
24:38With little to protect them, some of the gun crews suffered heavy casualties.
24:43Everything was blown to bits.
24:51There were pieces of machine gun everywhere with human flesh stuck to them.
24:56I could not believe they were parts of human beings.
24:58Bob Freely was a 22-year-old pilot flying an Avenger torpedo bomber that day.
25:06The sky is so big up there, I don't see all the fighters.
25:09I don't have time to look around to see anybody else because everything happens like that.
25:15What he did see was a giant battleship below.
25:20The Musashi has 11 planes coming in on it.
25:24You're coming down, then you start leveling off.
25:28And all this time they're shooting at you, and you don't know whether this bullet's going to hit you or...
25:34So you get about the distance that you think you should be at the altitude you should be.
25:39Open your bomb bay doors, and you're all set. Boom.
25:45His rear gunner watched as their 2,000-pound torpedo slammed into Musashi's port side.
25:52The torpedo bomber is the most effective weapon against a battleship
25:57because it can release something that carries a great deal of punch.
26:01The American Mark 13 torpedo carried a warhead of 600 pounds of high explosive.
26:05That was enough for us to punch through an armor belt.
26:11Musashi withstood the initial American assault, but the attacks kept coming.
26:20The fleets that are there at Leyte consist of multiple aircraft carriers.
26:25It's mind-boggling by today's standards how many ships were there.
26:28And so as a result of that, they could continue to attack and attack and wave after wave coming in.
26:37During the last wave, an American pilot took his memorable series of photographs.
26:47The relentless onslaught began to take a toll.
26:50When the Musashi loses speed and falls behind, then it's obvious that she's damaged.
26:59So now is the moment to close in for the kill.
27:05Lionel Gilbo was the rear gunner in the Helldiver bomber.
27:08My father dive-bombed the butto ship with a 2,000-pound ohmophelesen bomb right down the stack.
27:21These particular ships, very formidable ships, but they also made very large targets that were easily identified.
27:28And I think that's one of the reasons a lot of the aviators concentrated on Musashi.
27:32And she paid the price as a result.
27:35Yamato escaped the onslaught.
27:38But at 7.39 p.m., four hours after the final attack,
27:43Musashi, crippled yet miraculously still in one piece, rolled over and sank.
27:55Hundreds of people are crying for help in horrified voices as they were all sucked into the waves.
28:02In the pitch darkness of the deep sea, the ROV pilot carefully maneuvers his vehicle.
28:24We came across some very small pieces of debris, which looked the right age, looked the right material, but we weren't quite certain.
28:32Everybody was pretty much running on adrenaline at that time. It was very exciting.
28:37The ROV moves slowly through this unfamiliar landscape.
28:43It took about, I guess, a half hour or 45 minutes before we started getting into the heavier debris, and then it became more and more obvious.
28:52More and more obvious.
28:53You see them, right?
28:54You see them, right?
28:58That's Japanese.
29:00It's a Japanese warship.
29:02The minute we found the valve that had the kanji writing on it, it was like, okay, this is Japanese. Now all we have to do is prove that it's the Musashi.
29:10To do that, they need to find the ship's bow.
29:17There's bollocks.
29:18There's bollocks.
29:19There's bollocks.
29:20They're not too far away.
29:22They'll be above the, uh, the Musashi table.
29:25Something's there.
29:26It's there.
29:27It's there.
29:28The gold paint is gone, but the outline of the Imperial Japanese flower emblem is still there.
29:44As soon as we found the chrysanthemum on the bow, we knew what we were looking at.
29:50That's, that's proof of positive.
29:53There wasn't the kind of, you know, jumping up and shouting for joy that I've, I've experienced in the past.
29:58It was, uh, sort of a quiet relief that we had finally done it.
30:04At long last, Musashi is found.
30:08But a new and still more intriguing mystery is about to emerge.
30:12Over the next week, the search team explores the wreck of the super battleship.
30:22There's some shelves on the top.
30:25I think there's another one of the mounts for a light or a...
30:31Seventy years after she disappeared, they're compiling the first detailed picture of a lost technological marvel.
30:38Because there are no drawings for this ship and there's only a handful of photographs.
30:43So we're the first people really to document what she looks like.
30:48They also find signs of those who sailed her.
30:53A shoe.
30:55A helmet.
30:57And something unexpected on a warship.
31:00That's film.
31:02That is a film strip.
31:04It's not just a metal ship.
31:05These are crew that served in it.
31:07And some obviously died on the site as well.
31:09So it's important to document that.
31:17Musashi lies a good distance from the sinking position reported by the destroyer Kiyoshimo.
31:26But that's not the only reason she was so hard to find.
31:31The Musashi is literally on the side of a volcano.
31:34And if you've hiked up a volcano before, you know there's great big huge rocks and outcroppings and boulders.
31:40And so it's hidden inside the geology.
31:44The difficulty in finding the wreck is also explained by her shocking condition.
31:49Just the complete and utter destruction of the ship itself.
31:57The stern and the bow sections are really the only whole parts of the hull that remain.
32:03The bridge is somewhat intact from what we can see.
32:07But the rest, you know, the center section of the ship was just completely destroyed.
32:11So essentially, it's broken its back in at least two different locations.
32:17And for a ship that withstood so many attacks from torpedoes and bombs and essentially sank intact, that's more than I expected.
32:27What then could have caused such widespread destruction?
32:33It's a question which so far has no answer.
32:40One of the last pieces to be discovered is Musashi's most potent weapon.
32:45Which is obviously what caught everybody's imagination, these special 18-inch guns.
32:55These guns are held into the body of the ship, into the barbettes, by gravity alone.
33:00So when the ship capsizes, they're incredibly heavy objects that just fall out to their own weight.
33:06We found one of these guns after a week of searching.
33:09By now, the expedition has assembled an extensive record of Musashi.
33:16Over a hundred hours of video footage alone.
33:21We want to make sure that we have fully documented the condition and the state of the wreck so we can share that with everybody.
33:28And, you know, what we've done here and the data that we've gathered will provide the clues that people can use to recreate or have an understanding of what actually happened.
33:36The search team has opened a door.
33:42Now, others must step in to unravel Musashi's final hours.
33:47In March 2016, a group of Japanese experts assembles in Tokyo to take up the challenge.
33:55To help them, the Japanese broadcaster, NHK, has created a valuable tool.
34:08Like pieces of a gigantic puzzle, it's taken the hours of digital images gathered by the search expedition,
34:14painstakingly piecing them back together and creating a unique 3D model of the wreck.
34:23Only now is Musashi's enormous size apparent.
34:33At 263 meters, some 900 feet, she's longer than three jumbo jets.
34:37To begin with, these experts want to find out why a ship so many believed unsyncrasy is.
34:56should fail its first serious test.
35:11What is that thing that looks like a hole?
35:15Musami Teizuka has been studying the Musashi for 30 years.
35:22He believes he's identified one clue.
35:25A damaged section protruding from the port bow, most likely caused by a torpedo strike.
35:32Musashi would lose speed as a result, making it difficult to steer her.
35:39From an attacker's point of view, a battleship that's dragging would have been easier to hit with bombs or torpedoes.
35:46The last photo of Musashi shows her down at the bow, leading to the belief that flooding here caused her to sink.
35:56But a new scientific investigation at the University of Kobe tells a different story.
36:04Professor Hirotata Hashimoto, a specialist in naval architecture, conducted the analysis.
36:13When he simulates flooding inside the bow, the ship does pitch forward.
36:19But results show watertight compartments in the rest of the ship would not have been affected.
36:26Even if the bow, including the part protected by armor plating,
36:33is completely filled with water, the ship will still be left with enough buoyancy.
36:39So this flooding alone definitely could not have caused the ship to sink or capsize.
36:45To find answers to why Musashi sank, these experts will have to look elsewhere.
36:52Starting in the place where Musashi was constructed.
36:56At the Mitsubishi shipyard in Nagasaki, the Japanese team makes an important discovery.
37:06A file marked Musashi is uncovered in the company archives.
37:12It contains more than 200 pages of never before released original blueprints.
37:18By comparing images of the scattered pieces of the wreck with the blueprint, the team is able to identify them.
37:32A pump, a boiler, all parts protected by the heavy steel armor intended to make Musashi unsinkable.
37:45So the biggest question is, where did the armor go?
37:51In the high-resolution sonar image of the debris field, one structure attracts their attention.
37:58Examining video footage from the area, they discover a 90-foot piece of steel.
38:04It looks like part of the missing armor.
38:07When they match it up to the 3D model, they find it comes from the hull on the port side.
38:15But how did it come loose?
38:18Musashi's armor belt was so thick that everyone felt very confident on board the ship that they could stand up to the punishment of any weapon that could be thrown at it.
38:27But whereas ships making use of thinner plate could be welded, Musashi's armor could not be welded. It was simply too thick.
38:36And so they turned back to the 19th century and simply hot riveted the plates together.
38:40A company that took part in riveting the armor for Musashi is still operating in Osaka.
38:49Two workers recreate the technique used at the time to join these two pieces of armor plate.
38:56A special hammer drives the rivet into place.
39:11Japanese sailors assigned to Musashi had great confidence in the ship.
39:16They thought it was unsinkable, and that's because above deck they saw nothing but guns and firepower.
39:20But then below deck they were aware that the ship had the thickest armor of any warship in the world.
39:26But the Japanese investigation team doesn't share the sailors' confidence.
39:34I think rivets were the problem. No matter how thick the armor plates were, they wouldn't last once the rivets came loose.
39:41Musashi's armor was attached at a slanting angle to deflect incoming shells.
39:47She was built to withstand artillery duels against other battleships.
39:54But instead, she was hit by torpedoes and aerial bombs, which weren't weapons she expected to face when she was designed.
40:06If a torpedo from an attacking aircraft struck a joint in the armor plate,
40:11it could cause rivets to fail and seawater to begin to seep in.
40:15So how did this apparent vulnerability to torpedo strikes go unnoticed?
40:24The team discovers early concerns about this possible design flaw.
40:29A former officer on Musashi, who earlier served on her sister ship Yamato, made this recording before he died.
40:43I heard from Yamato's crew that during a torpedo attack, although the armor remained intact, the rivets were blown off and gradually water started to leak in around the joints.
41:03It made me realize, if we were hit by a lot of torpedoes, there would be more flooding, and that could be her weakest point.
41:12Shigeru Makino, a naval designer who oversaw the construction of Musashi, reported similar misgivings.
41:20But later wrote, the naval authorities decided to simply patch the armor joint, rather than find a permanent solution to the problem.
41:30In the minds of Musashi's 2400 crewmen, many still in their teens or early 20s, the Imperial Japanese Navy instilled a beguiling illusion.
41:42Their super battleship was quite simply unsinkable.
41:51One of them, Masahiro Oesi, believed it to the very end.
41:57Right up until the moment it sank, I didn't think it could happen.
42:01The Musashi wouldn't even budge an inch with a torpedo or two striking her.
42:06There would be no flooding, so we were told.
42:11Musashi also proved vulnerable to another unanticipated weapon, armor-piercing bombs from the air, as the search team discovered.
42:22Underwater footage revealed one of several three-foot holes rupturing the ship's deck.
42:35In a short section of the bow, we saw the damage from the bombs.
42:38That's corroborating what the U.S. pilots were telling us about the hits they were getting on Musashi.
42:44These weapons, although they are as crude and as simple as they can be, send through the air column, penetrate decks, and can explode below deck.
42:54This, in the end, causes great destruction on Musashi.
43:01Now, thanks to the 3D model of the wreck, the full extent of that destruction can be seen, especially up on the bridge, where the captain and many of his officers were stationed.
43:12A gaping 20-foot hole gouged into the starboard side marks where a bomb struck.
43:24One crew member up here miraculously survived.
43:29Kenji Atsuka remembers what happened.
43:32All the desks, chairs, everything flew to the port side.
43:42Bodies of those who were killed were piled up there too.
43:46The blast wave knocked us over, killing some.
43:49One man lost everything from his neck up, sitting in a chair about 10 feet from where I was.
43:55He was just dead.
44:01Standing on an open observation deck, Captain Inoguchi suffered a shrapnel wound in the shoulder.
44:08Protected from the fire himself, crewman Kotaki observed what happened.
44:13I saw him from behind.
44:17He was covering his shoulder with his hand like this, holding binoculars like this, and giving commands.
44:24Any ordinary person would have collapsed from such injuries.
44:28I thought, that's a true commander.
44:30Like her brave captain, Musashi sustained multiple hits from weapons she was never designed to face.
44:39Incredibly, her unusual strength allowed her to go down in one piece, leaving one final question.
44:47What tore her to pieces as she sank?
44:49That's a 46 centimeter shell underneath there, right?
44:58When the search team originally discovered Musashi...
45:01The turret housing was blown away.
45:04They couldn't believe the wreckage was spread over such a wide area.
45:10A square kilometer, more than half a square mile.
45:14Most of the shipwrecks that I've done are in deeper water than this.
45:17And we're seeing debris fields of 300 meters, 400 meters.
45:21So to see one twice or three times that size is really telling me that not only are we dealing with a large ship,
45:27but a large ship that has been blown apart.
45:30How does a ship that left the surface intact now lie shattered over the ocean floor?
45:37The Japanese team is determined to find an answer to this final mystery of Musashi.
45:43I'm not sure if it came from a boiler or something else, but is it possible this damage was caused by steam exploding?
45:53One member doesn't think so.
45:56Masatake Yoshida has been studying explosives for over 30 years.
46:01He believes something else tore Musashi apart.
46:04I can't think of any explanation besides a gunpowder explosion.
46:12If an explosion like that occurred, their internal parts would have shattered into many pieces.
46:16But where did this massive explosion take place?
46:22One piece of debris in particular has caught Yoshida's attention.
46:27Although mangled almost beyond recognition, it's part of the magazine holding the shells for one of Musashi's main guns.
46:37Thick steel like this wouldn't have ended up being so badly twisted if the ship had just sunk.
46:49Since Musashi fired her main guns only a handful of times during her final battle,
46:55an estimated 160 shells and 100 tons of gunpowder were still stored inside her.
47:01Suspicion as to where the explosion occurred falls on the second main gun.
47:11And first-hand reports David Mearns uncovered seem to support it.
47:17To see that level of damage on the seafloor tells me only one thing,
47:21that the Japanese survivors who heard explosions as it was capsizing,
47:26those explosions were actually magazine explosions.
47:28In the final moments, as Musashi healed over and sank,
47:34a few eyewitnesses aboard a nearby destroyer reported seeing the flash from a small explosion.
47:41Which means that some fires were already burning inside her.
47:47That makes me think that initial combustion rapidly spread into an explosion.
47:51Gunpowder contains some oxygen, so even underwater where there's none,
47:58under the right conditions, a combustive explosion can occur.
48:02To test his hypothesis, Dr. Yoshida ran a computer simulation.
48:07It clearly shows a ship made of heavy steel would have suffered catastrophic damage
48:14from an explosion below her second main gun.
48:19The ship's core would have splintered into hundreds of small pieces,
48:25with only the bow and stern remaining relatively intact.
48:29The high-resolution sonar map confirms this is how the wreck rests on the seafloor.
48:44David Mearns believes other factors also contributed to the massive damage sustained by Musashi.
48:49They see that a large section of the bow was imploded.
48:57And we can look at the drawings and know that there's watertight compartments in there,
49:01and they've squeezed as the ship sank very quickly.
49:04As Musashi plummets to the bottom,
49:08a crushing pressure equivalent to the weight of a car bears down on every square inch.
49:14When it hits the seabed, it's hitting the seabed actually at very high speed,
49:19probably minimum of 15 knots, maybe as much as 25 knots,
49:23and there's impact damage.
49:25And all of this was evident in one section of the bow.
49:30Somewhere in Musashi's twisted remains lies her captain, Toshihira Inoguchi.
49:36He went down with his ship after handing over his final report.
49:45In it, he wrote,
49:47I am truly glad that the other battleships suffered almost no damage.
49:52And I feel some consolation in thinking that Musashi was able to assume the role of a victim.
49:58Musashi bore the brunt of the American air assault on October 24th, 1944,
50:11leaving most of Japan's center force unscathed, including the super battleship Yamato.
50:19Undetected, Admiral Kurita and his 20 remaining ships steamed through the night.
50:32Heading for the American landing site at Leyte.
50:38To catch the defending force from 7th Fleet by surprise.
50:41On October 25th, led by the super battleship Yamato,
50:49the Japanese Navy launched the decisive surface attack it had long sought.
50:55But a bold strike by American destroyers and destroyer escorts managed to confuse the Japanese commander.
51:02And so, Admiral Kurita makes the fateful decision to reverse course, and in so doing, he walks away from what would have been the most lopsided victory of the Japanese Imperial Navy in the Second World War.
51:20Japan's Navy had gambled on winning the world's biggest sea battle to bring America to the negotiating table.
51:30But they made a fatal miscalculation.
51:33Surface ships with big guns were no longer the dominant force at sea.
51:41In the age of the battleships, the building and the loss of the Musashi is the end point.
51:45They weren't going to be defeated by another battleship, another great battleship, but by aircraft.
51:51And that's when the era of aircraft carriers took off.
51:54On October 24th, 2016, at Yasukuni Shrine in Tokyo, surviving crew members from Musashi gather to remember their lost comrades.
52:15The discovery of the wreck and the evidence it reveals of Musashi's vulnerability is a cruel reminder.
52:25This was not the unsinkable battleship they were led to believe her to be.
52:30But for crewman Sakuda, the wreck still bears an important message.
52:36I think the Musashi would like the people to know how bravely her crew members fought and died.
52:47What an astonishing battleship she was.
52:50How she fought and met her tragic end in the emptiness of war.
52:55I think those are the messages that the Musashi wants to send us.
52:59For Bob Freely, an American pilot who launched one of the many torpedoes that sank her,
53:09Musashi's discovery stirs thoughts of reconciliation.
53:14I don't want any Japanese survivor to think that I'm trying to laud these medals over them.
53:20Our opportunity is we have a common ground.
53:24They are survivors of the same action that I am a survivor of.
53:29And I'd just like to say, welcome brother.
53:33When we're going down of the sun, and in the morning, we will remember them.
53:48We will remember them.
53:51Above the wreck site in the Cebuyan Sea, the crew of the octopus pay their own final respects.
53:57It is a war grave.
54:00You know, we as sailors and seafarers ourselves, we have a lot of respect for what happened here.
54:08Instead of warplanes, they launch a flight of paper cranes.
54:13Symbol of the peace that has endured for three quarters of a century between once bitter enemies of World War II.
54:27By the end, I'd just read them, and generally understand the ship turning the ship and walk around the CU Nicole to the Bürgerza were sustained bullpen.
54:33By the end of the lend coisas, theered ship wrap with worry, around theدي them express themselves.
54:37Any air bag driver requires the desire to settle the命 hospitals, just recognize the m 마스크를 driving the armor on the roof.
54:41Not before the spacecraft.
54:45I see myself getting a tour where today, the printer were just met us in the air.
54:48Cause I can capture the fact of what occurred during my theme life.
54:50But before the end, the moonlight and the空 are the tava theской trek and its full,
54:54before we have to rest and then get to the extent.
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